The present invention relates to a manually actuatable electric pushbutton switch that automatically returns to the starting position after actuation, especially such a switch for the keyboard of an electronic device. The switch has a plastic housing in which is disposed a plate spring and on which is displaceably disposed an actuating button that cooperates with the plate spring, whereby the actuating button, during actuation, flexes a first region of the plate spring to establish electrical contact.
DE-OS 35 30 050 discloses a key module for foil keys. Disposed in a plastic housing is a plate spring that is bent at an obtuse angle in such a way that one leg extends essentially parallel to the base of the plastic housing, while the other leg projects freely into the interior of the housing. The plate spring is fixed within the housing by a right-angled projection of that leg that extends parallel to the base of the plastic housing, with this projection being adjustably held in place in a receiving slot of the housing. The edge region between the two legs of the plate spring defines the electrical contact position. For this purpose, displaceably disposed in the plastic housing is an actuating button that can be displaced against the force of a helical spring and that is in engagement with the upper, free end of the angled-off leg. When this actuating button is pressed downwardly, the edge region between the two legs is correspondingly moved downward in such a way that two superimposed switching foils are brought into contact with one another. After the actuating button is released, the switch returns to its starting position.
The drawback of this heretofore known key module is the uniform shape and orientation of the plate spring that triggers the electrical contact, since the user never knows exactly whether or not the key was correctly pressed and if the control function has been triggered.
DE-PS 912 597 discloses a switching key. Disposed on a base plate is a spring plate that comprises an essentially rectangular strip of resilient material. This spring plate has two elongated slots. In order to effectively shorten the length of the spring plate and to arch the central portion of the spring plate between the slots, the spring plate is arched on both sides of the slots. The front end of the spring plate, which is disposed on the base plate in this manner, thereby forms the contact location in cooperation with a second contact portion that is secured to the base plate. To actuate the switching key, an actuating element is associated with the spring plate. As this actuating element is being pressed down, the peak of the spring plate arch that is formed by the slots shifts in the direction of the free end of this spring plate in a movement that resembles t he propagation of waves. At a specific position of the actuating element, the spring plate then trips over and hence establishes the contact with the second contact portion of the base plate. Also with this heretofore known arrangement the user never knows for sure whether the switch has been correctly actuated and if the control function has been triggered.
It is an object of the present invention to improve an electric pushbutton switch of the aforementioned general type in such a way that the control reliability is improved.